Method and device of diagnosing bone strength

ABSTRACT

A bone strength diagnostic device includes a wave-transmission module for deriving a speed of sound that transmits an ultrasonic wave from a wave-transmission transducer for deriving the speed of sound obliquely to a bone covered with soft tissues; a wave-reception module for deriving the speed of sound that receives, with a plurality of wave-reception transducers for deriving the speed of sound, the ultrasonic wave that exits from the bone to the side of the soft tissues, the ultrasonic wave being received after it is transmitted from the wave-transmission module for deriving the speed of sound and propagating along a front surface of the bone; a shape detection module for detecting the shape of the front surface of the bone; and a speed-of-sound deriving module for deriving the speed of sound of the ultrasonic wave that propagates along the front surface of the bone, based on the received wave signals, using the wave-reception module for deriving the speed of sound, and the shape of the front surface of the bone detected using the shape detection module.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2008-191694, which was filed on Jul. 25, 2008, theentire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a method and device of diagnosing bonestrength by transmitting an ultrasonic wave that propagates at the speedof sound along a bone surface.

BACKGROUND

Speed of sound of an ultrasonic wave that propagates inside of a bonecan be used for an index of diagnosing bone strength. Conventionally,devices have existed that measures the speed of sound of the ultrasonicwave that propagates along the surface of a long pipe-shaped bone (i.e.,long bone) in the longitudinal direction to diagnose bone strength basedon the speed of sound.

As devices for measuring the speed of sound of the ultrasonic wavepropagating along the bone surface, as shown in FIG. 17A, a device 901including a transducer 902 for wave transmission and two transducers 903and 904 for wave reception is well-known. The device 901 measures thespeed of sound by the following method assuming that the bone surface isflat, as well as the surface of soft tissues, such as muscles coveringthe bone, being parallel to each other.

First, the transducer 902 for wave transmission transmits an ultrasonicwave to be incident to the bone surface near a critical angle togenerate a surface wave on the bone surface. The surface wave propagatesalong the bone surface while emitting a leaky surface wave at apredetermined angle (same angle as the critical angle). The leakysurface wave is received by the two transducers 903 and 904 for wavereception. Because the interval between the two transducers 903 and 904for wave reception is known, the speed of sound of the surface wave canbe calculated from a time difference between the times when thetransducers 903 and 904 received the leaky surface wave, respectively.

However, the bone surface and the surface of soft tissues may not beparallel to each other and, thus, in that case, the device 901 mayproduce errors in its calculation results. There are various devicesproposed to eliminate the errors (for example, refer toJP2003-517328(A), WO03/099132, and WO03/099133).

As one particular example of such devices, as shown in FIG. 17B, aspeed-of-sound measuring device 901′ includes two transducers 902 and905 for wave transmission, and two transducers 903 and 904 for wavereception. The device 901′ transmits an ultrasonic wave from thetransducer 902 for wave transmission, and receives a leaky surface waveproduced due to the transmission with the two transducers 903 and 904for wave reception. Further, an ultrasonic wave is similarly transmittedfrom the transducer 905 for wave transmission, and the two transducers903 and 904 for wave reception receive a leaky surface wave produced dueto the transmission.

The speed of sound of the surface wave can be calculated inconsideration of inclination of the bone surface by using a timedifference between wave-reception timings of the leaky surface wave bythe two transducers 903 and 904 for wave reception when the ultrasonicwave is transmitted from the transducer 902 (or 905) for wavetransmission, and by using a difference between a propagation time froma wave transmission to a wave reception when the ultrasonic wave istransmitted from the transducer 902 for wave transmission and the leakysurface wave is received by the transducer 903 (or 904) for wavereception and a propagation time from a wave transmission to a wavereception when the ultrasonic wave is transmitted from the transducer905 for wave transmission and the leaky surface wave is received by thetransducer 903 (or 904) for wave reception.

Further, JP2003-517328(A) discloses, in addition to the speed-of-soundmeasuring device equipped with two transducers for wave transmission andtwo transducers for wave reception as the device 901′ described above, aspeed-of-sound measuring device including an arrayed transducerincluding a plurality of transducers. This device first transmitsultrasonic waves from the arrayed transducer to a bone, and thenreceives reflected waves from a surface of the bone. The device carriesout imaging of a shape of the bone front surface by a known method basedon the received wave signals, and then derives the thickness of softtissues.

The device calculates from the thickness of soft tissues an optimumspaced distance between the transducers for wave transmission and thetransducers for wave reception. When the soft tissues are thick, if theinterval between the transducers for wave transmission and thetransducers for wave reception is too near, leaky surface waves cannotbe received. On the other hand, when the soft tissues are thin and theinterval between both transducers is too far, only leaky surface wavesof small amplitude can be received and, therefore, it may not bedesirable. Thus, the optimum distance between the transducers for wavetransmission and the transducers for wave reception may vary dependingon the thickness of soft tissues.

Next, the device determines two transducers for wave transmission andtwo transducers for wave reception to be used for a speed-of-soundmeasurement based on the calculated optimum spaced distance between thetransducers for wave transmission and the transducers for wave receptionamong transducers constituting the arrayed transducer. Then, the devicecalculates a speed of sound of the surface wave using the fourdetermined transducers.

However, the device 901′ or the device disclosed in JP2003-517328(A),WO03/099132, and WO03/099133 calculates a speed of sound based on thepropagation course of the ultrasonic wave when the bone surface is flat.Thus, the device can only be applied when the bone surface is flat.Therefore, errors will be greater when a shape of an actual bone surfaceis curved (for example, when a circumferential speed of sound of a longpipe-shaped bone is measured).

Further, the speed-of-sound measuring device including the arrayedtransducer disclosed in JP2003-517328(A) acquires the shape of the bonefront surface in an image, using the arrayed transducer. However, thisimage is only originally used to detect the thickness of soft tissuesand determine four transducers to be used for a speed-of-soundmeasurement among the arrayed transducers based on the thickness and,thus, it is not for calculation of a speed of sound.

SUMMARY

Therefore, the present invention is made to address these situations,and provides a bone strength diagnostic device with a high diagnosticaccuracy of bone strength, which can derive the speed of sound of anultrasonic wave propagating along a bone surface with sufficientaccuracy even if the shape of a bone front surface is curved.

According to an aspect of the invention, a bone strength diagnosticdevice includes a wave-transmission module for deriving a speed of soundthat transmits an ultrasonic wave from a wave-transmission transducerfor deriving the speed of sound obliquely to a bone covered with softtissues, a wave-reception module for deriving the speed of sound thatreceives the ultrasonic wave that exits from the bone to the side of thesoft tissues with a plurality of wave-reception transducers for derivingthe speed of sound, the ultrasonic wave being received after it istransmitted from the wave-transmission module for deriving the speed ofsound and propagates along a front surface of the bone, a shapedetection module for detecting the shape of the front surface of thebone, and a speed-of-sound deriving module for deriving the speed ofsound of the ultrasonic wave that propagates along the front surface ofthe bone, based on the received wave signal by the wave-reception modulefor deriving the speed of sound, and the shape of the front surface ofthe bone detected by the shape detection module.

An ultrasonic wave is transmitted from the wave-transmission transducerfor deriving the speed of sound obliquely to a bone to generate anultrasonic wave that propagates along the bone front surface. Thisultrasonic wave exits from the bone to the side of the soft tissuesafter propagated along the bone front surface and is received by theplurality of wave-reception transducers for deriving the speed of sound.The speed-of-sound deriving module derives the speed of sound of theultrasonic wave that propagates along the bone front surface by usingthe wave signal received by the wave-reception module for deriving thespeed of sound and the shape of the bone front surface detectedbeforehand by the shape detection module, and then diagnoses the bonestrength based on the derived speed of sound.

Thus, even if the shape of the bone front surface is curved, by derivingthe speed of sound in the bone using the information on the shape of thebone front surface, the speed of sound in the bone can be derived withsufficient accuracy. As a result, the diagnostic accuracy of the bonestrength can be improved.

The wave-reception transducer for deriving the speed of sound mayinclude a plurality of wave-reception transducers for deriving the speedof sound. A sound insulating material may be arranged between thewave-transmission module for deriving the speed of sound and theplurality of wave-reception transducers for deriving the speed of sound.

The shape detection module may include a wave-transmission module forshape detection that transmits the ultrasonic wave to the bone, awave-reception module for shape detection that receives a front-surfacereflected wave of the ultrasonic wave from the front surface of thebone, the ultrasonic wave being transmitted from the wave-transmissionmodule for shape detection, and a front surface shape detecting modulefor detecting the shape of the front surface of the bone using the wavesignal received by the wave-reception module for shape detection.

The wave-transmission module for shape detection may include a pluralityof wave-transmission transducers for shape detection that transmit theultrasonic waves simultaneously; and the wave-reception module for shapedetection includes a plurality of wave-reception transducers for shapedetection that receive the front-surface reflected wave. The frontsurface shape detecting module may include an incoming directiondetecting module for detecting the incoming direction of thefront-surface reflected wave to each transducer group using a timedifference between times when two wave-reception transducers for shapedetection constituting each transducer group receive the front-surfacereflected wave, each transducer group including adjacent twowave-reception transducers for shape detection among the plurality ofwave-reception transducers for shape detection, a propagation timedetecting module for detecting a propagation time of the front-surfacereflected wave that reaches each transducer group using the receivedwave signal of the front-surface reflected wave of at least onewave-reception transducer for shape detection among the twowave-reception transducers for shape detection constituting eachtransducer group, a front-surface reflection point detecting module fordetecting a reflection point of the ultrasonic wave on the front surfaceof the bone based on the incoming direction and the propagation time ofthe front-surface reflected wave detected for each transducer group bythe incoming direction detecting module and the propagation timedetecting module, respectively, and a shape deriving module for derivingthe shape of the front surface of the bone using the plurality ofreflection points on the front surface of the bone, the reflectionpoints being detected for the plurality of transducer groups havingdifferent transducers by the front-surface reflection point detectingmodule.

The wave-transmission transducer for shape detection may function as thewave-reception transducer for shape detection as well.

The wave-reception transducer for deriving the speed of sound mayfunction as the wave-reception transducer for shape detection as well.

The shape detection module may perform detection of a shape of a backsurface of the bone in addition to the detection of the shape of thefront surface of the bone.

The wave-reception module for shape detection may perform wave receptionof the back-surface reflected wave from the back surface of the bonethat reaches the plurality of wave-reception transducers for shapedetection after the front-surface reflected wave in addition toperforming the wave reception of the front-surface reflected wave. Theincoming direction detecting module may perform detection of an incomingdirection of the back-surface reflected wave to each transducer groupusing a time difference between times when the two wave-receptiontransducers for shape detection constituting each transducer groupreceives the back-surface reflected wave in addition to performingdetection of the incoming direction of the front-surface reflected wave.The propagation time detecting module may perform detection of thepropagation time of the back-surface reflected wave that reaches eachtransducer group using the received wave signal of the back-surfacereflected wave of at least one wave-reception transducer for shapedetection among the two wave-reception transducers for shape detectionconstituting each transducer group in addition to performing thedetection of the propagation time of the front-surface reflected wavethat reaches each transducer group. The shape detecting module mayinclude a back-surface reflection point detecting module for detecting areflection point of the ultrasonic wave on the back surface of the bonebased on the incoming direction and the propagation time of theback-surface reflected wave detected for each transducer group by theincoming direction detecting module and the propagation time detectingmodule, and the shape of the front surface of the bone derived by theshape deriving module. The shape deriving module may derive the shape ofthe back surface of the bone with the back-surface reflection pointdetecting module using the plurality of reflection points on the backsurface of the bone that are detected for the plurality of transducergroups having different transducers.

The bone strength diagnostic device may further comprises a dampingcoefficient detecting module for detecting a damping coefficient of theultrasonic wave received by the wave-reception module for deriving thespeed of sound based on the transmitted wave signal of thewave-transmission module for deriving the speed of sound and thereceived wave signal of the wave-reception module for deriving the speedof sound.

According to another aspect of the invention, a method of diagnosingbone strength includes detecting a shape of a front surface of a bonecovered with soft tissues, transmitting an ultrasonic wave obliquely tothe bone, receiving the ultrasonic wave that exits from the bone to theside of the soft tissues at a plurality of locations after it istransmitted and propagates along the front surface of the bone, andderiving a speed of sound of the ultrasonic wave that propagates alongthe front surface of the bone based on the received wave signal and thedetected shape of the front surface of the bone.

An ultrasonic wave is transmitted obliquely to a bone to generate anultrasonic wave that propagates along the bone front surface. Thisultrasonic wave exits from the bone to the side of the soft tissuesafter propagated along the bone front surface and is received by theplurality of locations. The speed of sound of the ultrasonic wave thatpropagates along the bone front surface is derived using the receivedwave signal and the detected shape of the bone front surface to diagnosethe bone strength based on the derived speed of sound.

Thus, even if the shape of the bone front surface is curved, by derivingthe speed of sound in the bone using the information on the shape of thebone front surface, the speed of sound in the bone can be derived withsufficient accuracy. As a result, the diagnostic accuracy of the bonestrength can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings, in which thelike reference numerals indicate like elements and in which:

FIGS. 1 and 1B are a schematic diagram showing a configuration of a bonestrength diagnostic device according to an embodiment of the presentinvention;

FIG. 2A is a schematic view for illustrating an ultrasonic wavetransmitted from an arrayed transducer, and FIG. 2B is a schematic viewfor illustrating propagation courses of the ultrasonic wave transmittedfrom the arrayed transducer;

FIG. 3 is a timing chart showing received wave signals of the arrayedtransducer;

FIG. 4 is a schematic view for illustrating propagation courses of theultrasonic wave transmitted from a transducer dedicated to wavetransmission;

FIGS. 5 and 5B are a flowchart showing an operation of bone strengthdiagnostic device;

FIG. 6A is a schematic view for illustrating a method of detecting afront-surface reflection point, and FIG. 6B is a schematic view forillustrating a method of detecting an incoming direction;

FIG. 7 is a schematic view for illustrating a method of detecting aback-surface reflection point;

FIG. 8 is a graph to be used for the detection of the back-surfacereflection point, showing a relation between a propagation time and aposition of the back-surface reflection point;

FIG. 9 is a schematic view for illustrating a method to identify atransducer which receives a leaky surface wave;

FIG. 10 is a graph for illustrating a method to distinguish a waveformof noise from a waveform of the ultrasonic wave;

FIG. 11 is a schematic view for illustrating a deriving method of aspeed of sound;

FIG. 12 is a schematic view for illustrating a deriving method of thespeed of sound according to Modified Embodiment 4;

FIG. 13 is a schematic view for illustrating a deriving method of thespeed of sound according to Modified Embodiment 5;

FIG. 14 is a graph to be used for deriving the speed of sound byModified Embodiment 5, showing a relation between an angle of incidenceand a propagation time;

FIGS. 15A to 15C are schematic views of arrayed transducers, where FIG.15A shows an arrayed transducer of Modified Embodiment 7, FIG. 15B showsan arrayed transducer of Modified Embodiment 8, and FIG. 15C shows anultrasonic transceiver having an arrayed transducer of ModifiedEmbodiment 9 added with a change-over circuit;

FIGS. 16A to 16C are views showing configurations of ultrasonictransceivers, where FIG. 16A shows an ultrasonic transceiver of ModifiedEmbodiment 12, FIG. 16B shows an ultrasonic transceiver of ModifiedEmbodiment 13, and FIG. 16C shows an ultrasonic transceiver of ModifiedEmbodiment 14; and

FIGS. 17A and 17B are schematic views showing conventionalspeed-of-sound measuring devices.

DETAILED DESCRIPTION

Hereinafter, embodiments of the invention is explained referring to theappended drawings.

Embodiment 1

A bone strength diagnostic device 1 of an embodiment of the inventionderives a speed of sound of an ultrasonic wave propagating along asurface of a bone to diagnose the strength of the bone based on thespeed of sound.

The bone strength diagnostic device 1 diagnoses a bone inside a bodysuch as, but not limited to, a cortical bone of long-pipe shape, such asa tibia, for example. Typically, a bone is configured with a corticalbone part and a cancellous bone part, in the shape of lattice-shapedspicules, existing in the inner side of cortical bone.

As shown in FIG. 1, a surface 10 a of a cortical bone 10 (hereinafter,simply referred to as a “bone” in this embodiment) is covered with softtissues 11, such as muscles and fat.

FIG. 1 shows a cross-section perpendicular to the longitudinal directionof the bone 10 (i.e., transverse cross-section), and a shape of the bonefront surface 10 a is formed in a loosely curved surface which is convextoward the side of the soft tissues 11. In this embodiment, althoughillustration is omitted, the surface of the longitudinal cross-sectionof the bone 10 may be substantially flat and may be inclined withrespect to the surface of the soft tissues 11.

The bone strength diagnostic device 1 of this embodiment derives thespeed of sound of an ultrasonic wave propagating along the bone frontsurface 10 a in the circumferential direction (hereinafter, referred toas a “circumferential speed of sound”) and the speed of sound of anultrasonic wave propagating along the bone front surface 10 a in thelongitudinal direction (hereinafter, referred to as a “longitudinalspeed of sound”), and then diagnoses the strength of the bone using thespeeds of sound of these two directions.

As shown in FIG. 1, the bone strength diagnostic device 1 of thisembodiment includes an ultrasonic transceiver 2 and a device body 3. Thedevice body 3 includes, as shown in FIG. 1B, a transceiver separatingmodule 4, a transmission circuit 5, a transmission switching module 5 a,a plurality of reception circuits 6 a-61, an ultrasonic controllingmodule 7, a calculation module 8, and a display module 9.

The ultrasonic transceiver 2 transmits and receives an ultrasonic wave,and is contacted with a surface of the soft tissues 11. The surface ofthe transducer 2 contacted with the surface of the soft tissues 11 iscalled herein a “contacting face 2 a.” The ultrasonic transceiver 2includes a transducer 21 dedicated to wave transmission, an arrayedtransducer 22 having a plurality of transducers 22 a-22 l (twelvetransducers in this embodiment) arranged in a single row, and a soundinsulating material 23. The transducer used herein is such that itoscillates when an electric signal is applied to generate an ultrasonicwave from its surface (oscillating surface), and on the other hand, itgenerates an electric signal when it receives an ultrasonic wave on itssurface to be oscillated.

The transducer 21 dedicated to wave transmission, the sound insulatingmaterial 23, and the arrayed transducer 22 are aligned in the arrayeddirection of the arrayed transducer 22. When measuring thecircumferential speed of sound, as shown in FIG. 1, the bone ultrasonicwave transceiver 2 is contacted with the soft tissues 11 so that thearrayed direction of the arrayed transducer 22 is oriented substantiallyin the circumferential direction of the bone 10. On the other hand, whenmeasuring the longitudinal speed of sound, the ultrasonic transceiver 2is contacted the soft tissues 11 so that the arrayed direction of thearrayed transducer 22 is oriented substantially in the longitudinaldirection of the bone 10.

The transducer 21 dedicated to wave transmission is provided so that itssurface (oscillating surface) inclines to the contacting face 2 a. Asthe transducer 21 dedicated to wave transmission, what transmits anultrasonic wave with a wide directivity may be used (in other words,what has a wide angle range of emitting an ultrasonic wave). The smallerthe area of the oscillating surface, the wider the directivity becomes.That is, because sensitivity for the ultrasonic wave and the directivityhave a trade-off relation, the installation angle of the transducer 21dedicated to wave transmission and the dimension of the oscillatingsurface are designed suitable for the object to be measured.

The twelve transducers 22 a-221 that constitute the arrayed transducer22 are arranged so that their surfaces (oscillating surface) areparallel to the contacting face 2 a. Note that, although the number oftransducers that constitute the arrayed transducer 22 is twelve in thisembodiment, it may be any arbitrary number other than twelve. Ahorizontal length of the arrayed transducer 22 in the case of FIG. 1 maybe 24 mm, for example.

In this embodiment, the sound insulating material 23 is formed in aplate shape and is arranged between the transducer 21 dedicated to wavetransmission and the arrayed transducer 22. The material of the soundinsulating material 23 may be a material having a sound absorbingfunction, such as cork, a synthetic rubber, a porous material (forexample, a foamed resin material), etc. The sound insulating material 23prevents the ultrasonic wave transmitted from the transducer 21dedicated to wave transmission from propagating inside of the ultrasonictransceiver 2 to directly reach the arrayed transducer 22. In otherwords, it can prevent that an ultrasonic wave unnecessary for deriving aspeed of sound in the bone is received by the arrayed transducer 22.

Note that a coupling material (not illustrated) intervenes between thecontacting face 2 a and the surface of the soft tissues 11. The couplingmaterial prevents a gap from being produced between the contacting face2 a and the surface of the soft tissues 11. In addition, the couplingmaterial adjusts acoustic impedances of the transducers 22 a-221 and thesoft tissues 11 to suppress the ultrasonic wave transmitted from thetransducer 21 dedicated to wave transmission or the arrayed transducer22, reflecting on the surface of the soft tissues 11.

The transducer 21 dedicated to wave transmission is connected to thetransmission circuit 5 via the transmission switching module 5 a. Theplurality of transducers 22 a-221 are connected to the transmissioncircuit 5 via the transceiver separating module 4 and the transmissionswitching module 5 a. The transmission circuit 5 generates an electricpulse signal to be transmitted to the transmission switching module.Note that a chirp signal may be used instead of the electric pulsesignal. The center frequency of the electric pulse oscillation may beapproximately 1 to 10 MHz, for example.

The transmission switching module 5 a transmits the electric pulsesignal transmitted from the transmission circuit 5 to any of thetransducers 21 dedicated to wave transmission and the arrayed transducer22. The transmission switching module 5 a changes over the transducersto select one that transmits an ultrasonic wave.

The twelve transducers 22 a-22 l that constitute the arrayed transducer22 are connected to twelve reception circuits 6 a-6 l via thetransceiver separating module 4, respectively. The reception circuits 6a-6 l perform a process, such as an amplifying process, a filteringprocess, a digital conversion process of the electric signal transmittedfrom the transducers 22 a-22 l, respectively (of the received wavesignal), and then transmit it to the calculation module 8.

The transceiver separating module 4 prevents the transmitted wave signalsent to the arrayed transducer 22 from the transmission circuit 5(electric pulse signal) from flowing into the reception circuits 6 a-61directly, and prevents the received wave signal sent to the receptioncircuits 6 a-61 from the arrayed transducer 22 from flowing into thetransmission circuit 5.

The ultrasonic controlling module 7 is connected with the transmissioncircuit 5 and transmits a signal for transmitting ultrasonic waves fromthe twelve transducers 22 a-221 to the transmission circuit 5.

Note that the wave-transmission transducer for deriving the speed ofsound in the claims corresponds to the transducer 21 dedicated to wavetransmission. Further, the plurality of wave-reception transducers forderiving the speed of sound, the plurality of wave-transmissiontransducers for reflected waves, and the plurality of wave-receptiontransducers for reflected waves in the claims correspond to the twelvetransducers 22 a-221 that constitute the arrayed transducer 22.Therefore, in this embodiment, the wave-reception transducer forderiving the speed of sound serves as the wave-reception transducer forshape detection as well. Thus, the number of transducers that receivethe ultrasonic wave can be reduced. Further, in this embodiment, becausethe wave-transmission transducer for shape detection serves as thewave-reception transducer for shape detection as well, the number oftransducers used for the detection of the bone shape can also bereduced.

Further, in this embodiment, the wave-transmission module for derivingthe speed of sound in the claims includes the transducer 21 dedicated towave transmission and the transmission circuit 5. The wave-transmissionmodule for shape detection in the claims includes the arrayed transducer22 and the transmission circuit 5. The wave-reception module forderiving the speed of sound and the wave-reception module for shapedetection in the claims include the arrayed transducer 22 and the twelvereception circuits 6 a-61.

Hereinafter, an operation of the ultrasonic transceiver 2 will beexplained.

When Ultrasonic Wave is Transmitted from Arrayed Transducer 22

When the arrayed transducer 22 is determined by the transmissionswitching module 5 a to be a transducer that transmits an ultrasonicwave, an electric pulse signal is sent from the transmission circuit 5to the arrayed transducer 22. The transducers 22 a-221 that constitutethe arrayed transducer 22 transmit the ultrasonic waves of the samephase to the bone 10 simultaneously (incident wave). As shown in FIG.2A, the incident waves transmitted from the arrayed transducer 22propagate inside of the soft tissues 11 as a plane wave. This plane wavetravels in a direction perpendicular to the contacting face 2 a.

As shown in FIG. 2B, a part of the incident wave is reflected on thebone front surface 10 a. A front-surface reflected wave produced by thisis received by the transducers 22 a-221. On the other hand, another partof the incident wave that propagates inside of the bone 10 withoutreflecting on the bone front surface 10 a is reflected on the backsurface 10 b of the bone 10. The back-surface reflected wave produced bythis is received by the transducers 22 a-221 after the front-surfacereflected wave. Therefore, the front-surface reflected wave or theback-surface reflected wave received by each of the transducers 22 a-221may not be determined from which transducer transmitted.

Preferably, a spatial relationship from the arrayed transducer 22 to thebone front surface 10 a may be a short-distance field such that theplane wave transmitted from the arrayed transducer 22 propagates to thebone front surface 10 a without being spread. Thus, an accuracy ofdetecting the shape of the bone front surface 10 a can be improved.Preferably, the distance from the arrayed transducer 22 to the bone backsurface 10 b may also be close.

When the transducers 22 a-221 receive the front-surface reflected waveor the back-surface reflected wave, they converts the acoustic wave intoan electric signal, and then transmit the electric signal (received wavesignal) to the reception circuits 6 a-61 via the transceiver separatingmodule 4, respectively. Thus, the wave reception of the front-surfacereflected wave and the back-surface reflected wave is performedindependently by the transducers 22 a-221.

FIG. 3 shows an example of the received wave signals by the transducers22 a-221. The horizontal axis of FIG. 3 represents a time after thetransmission of the incident wave. A wavefront Ma in FIG. 3 representsthe front-surface reflected wave, and a wavefront Mb represents theback-surface reflected wave. The back-surface reflected wave may beinverted in phase because it reflects at the change of acousticimpedance from a coarse part (cancellous bone) to a dense part (corticalbone).

When Ultrasonic Wave is Transmitted from Transducer 21 Dedicated to WaveTransmission

When the transmission switching module 5 a determines the transducer 21dedicated to wave transmission to be a transducer that transmits anultrasonic wave, an electric pulse signal is sent from the transmissioncircuit 5 to the transducer 21 dedicated to wave transmission, and thetransducer 21 dedicated to wave transmission then transmits anultrasonic wave to the bone 10. As shown in FIG. 4, from the transducer21 dedicated to wave transmission, an ultrasonic wave with a widedirectivity (incident wave) is transmitted. The incident wave thatpropagates inside of the soft tissues 11 in a direction inclined to thecontacting face 2 a.

The ultrasonic wave transmitted from the transducer 21 dedicated to wavetransmission is received by the arrayed transducer 22 via a plurality ofpropagation routes. Like the case where an ultrasonic wave istransmitted from the arrayed transducer 22, the transducers 22 a-22 ltransmits the received wave signal to the reception circuits 6 a-6 l,respectively, when they receive the ultrasonic waves.

The following three types exist for the propagation routes of theultrasonic wave that is transmitted from the transducer 21 dedicated towave transmission and reaches the arrayed transducer 22. One route is apropagation route where an ultrasonic wave propagates along the surfaceof the soft tissues 11 and then reaches the arrayed transducer 22directly. Another route is a propagation route where an ultrasonic wavereflects on the bone front surface 10 a and then reaches the arrayedtransducer 22 (propagation route including the reflected wave 31 or thereflected wave 32 in FIG. 4). Still another route is the propagationroute where the ultrasonic wave propagates along the bone front surface10 a and after that, exits to the side of the soft tissues 11 from thebone 10 and then reaches the arrayed transducer 22. Two types amongthese three types of the propagation routes are explained below.

When a part of the incident wave is incident on the bone front surface10 a near at the critical angle, a surface wave will occur on the bonefront surface 10 a. This surface wave propagates along the bone frontsurface 10 a, while emitting a leaky surface wave in a predetermineddirection toward the soft tissues 11 (direction near at the criticalangle with respect to the bone front surface 10 a). This leaky surfacewave is received by the arrayed transducer 22. An ultrasonic wave 33 inFIG. 4 is shown as an example of the leaky surface wave. The criticalangle is determined based on the speed of sound in the soft tissues 11and the speed of sound in the bone 10. Because the transducer 21dedicated to wave transmission is used as a transducer with a widedirectivity, even if the inclination of the bone front surface 10 avaries depending on examinees, it is possible to make the ultrasonicwave be incident on the bone front surface 10 a near at the criticalangle.

When the part of the incident wave is incident on the bone front surface10 a at an angle smaller than the critical angle, it is refracted by thebone front surface 10 a and then propagates in the vicinity of the bonefront surface 10 a of the bone 10, and after that, it is again refractedby the interface 10 a of the bone 10 and the soft tissues 11. Thisrefracted wave (hereinafter, referred to as a “bone front-surfacerefracted wave”) is received by the arrayed transducer 22. An ultrasonicwave 34 in FIG. 4 is shown as an example of the bone front-surfacerefracted wave. The bone front-surface refracted wave is generated onlywhen the shape of the bone front surface 10 a is not flat.

Both the bone front-surface refracted wave and the leaky surface wavemay be received by a single transducer that constitutes the arrayedtransducer 22. The bone front-surface refracted wave may be receivedbefore or after the leaky surface wave is received.

When a bone width (a length of the bone 10 in the horizontal directionof FIG. 1) is small, the leaky surface wave may not reach a positionsufficiently distant from the transducer 21 dedicated to wavetransmission. That is, the smaller the bone width becomes, the shorterthe range within which the leaky surface wave can be received will be.Although it may depend on the inclination of the bone front surface 10 arelative to the contacting face 2 a, the distance between a transduceramong the transducers capable of receiving the leaky surface wave whichis the closest to the transducer 21 dedicated to wave transmission andthe transducer 21 dedicated to wave transmission will be longer as thethickness of the soft tissues 11 is thicker. In this embodiment, becausethe leaky surface wave is received by the plurality of transducers 22a-22 l, even if the bone width or the thickness of the soft tissues 11varies for individual examinees, it is possible to certainly receive theleaky surface wave by at least one of the plurality of transducers amongthe plurality of transducers 22 a-22 l.

As described above, the leaky surface wave can only be received at aposition with some distance from the transducer 21 dedicated to wavetransmission. On the other hand, the reflected wave from the bonesurface 10 a can be received even at a position close to the transducer21 dedicated to wave transmission. For example, in the case of FIG. 4,the leaky surface wave will be received by the transducer 22 d and thetransducers on the right of the transducer 22 d, but the reflected wavefrom the bone surface 10 a will be received by the transducer 22 a andthe transducers on the right of the transducer 22 a. Thus, thetransducers on the side of the transducer 21 dedicated to wavetransmission in the arrayed transducer 22 may receive only the reflectedwave, and may not receive the leaky surface wave.

When both the leaky surface wave and the reflected wave from the bonefront surface 10 a are received by one transducer constituting thearrayed transducer 22, the leaky surface wave is received before thereflected wave. This is because the speed of sound in the bone 10 isfaster than the speed of sound in the soft tissues 11.

An ultrasonic wave that propagates along the surface of the soft tissues11 and reaches the arrayed transducer 22 directly (hereinafter, referredto as a “direct wave”) reaches a transducer near the transducer 21dedicated to wave transmission before the leaky surface wave. However,the ultrasonic wave may reach after the leaky surface wave a transducerapart from the transducer 21 dedicated to wave transmission. Note that,due to the existence of the sound insulating material 23, the amplitudeof the direct wave is designed to be very small compared with theamplitude of the leaky surface wave or the reflected wave.

Referring back to FIG. 1B, the calculation module 8 includes a CPU, aRAM, and a ROM (these are not illustrated), and also includes a signalprocessing module 81, a shape detecting module 82, a speed-of-soundderiving module 83, and a bone strength index deriving module 84.

The signal processing module 81 includes a memory module and a signalprocessing circuit (these are not illustrated). The signal processingmodule 81 receives the received wave signals transmitted from thereception circuits 6 a-6 l and stores in the memory module the receivedwave signals within a predetermined period of time from the wavetransmission of the ultrasonic wave. The signal processing module 81then detects a peak value of the received wave signals with the signalprocessing circuit, and transmits it to the shape detecting module 82and the speed-of-sound deriving module 83.

The shape detecting module 82 detects shapes of the bone front surface10 a and the bone back surface 10 b by using the received wave signalsof the front-surface reflected wave and the back-surface reflected waveof the arrayed transducer 22 when the ultrasonic wave is transmittedfrom the arrayed transducer 22. The shape detecting module 82 includesan incoming direction detecting module 82 a, a propagation timedetecting module 82 b, a front-surface reflection point detecting module82 c, a shape deriving module 82 d, and a back-surface reflection pointdetecting module 82 e.

The incoming direction detecting module 82 a determines eleventransducer groups 22A-22K (refer to FIG. 1), each group having adjacenttwo transducers among the twelve transducers 22 a-22 l, and detectsincoming directions of the front-surface reflected waves and theback-surface reflected waves that reach each of the transducer groups22A-22K.

The propagation time detecting module 82 b detects a propagation time ofthe front-surface reflected wave and a propagation time of theback-surface reflected wave that reach each of the transducer groups22A-22K.

The front-surface reflection point detecting module 82 c detects elevenreflection points on the bone front surface 10 a (front-surfacereflection points) based on the incoming directions and the propagationtimes of the front-surface reflected waves which reached the eleventransducer groups 22A-22K and which are detected by the incomingdirection detecting module 82 a and the propagation time detectingmodule 82 b, respectively.

The shape deriving module 82 d derives a shape of the bone front surface10 a using the eleven front-surface reflection points detected by thefront-surface reflection point detecting module 82 c. Further, the shapederiving module 82 d derives a shape of the bone back surface 10 b usingthe eleven back-surface reflection points detected by the back-surfacereflection point detecting module 82 e described later, and also derivesa thickness of the bone 10 (cortical bone) based on the shapes of thebone front surface 10 a and the bone back surface 10 b.

The back-surface reflection point detecting module 82 e detects elevenreflection points on the bone back surface 10 b (back-surface reflectionpoints) based on the incoming directions and the propagation times ofthe back-surface reflected waves which reach the eleven transducergroups 22A-22K, respectively and which are detected by the incomingdirection detecting module 82 a and the propagation time detectingmodule 82 b.

The speed-of-sound deriving module 83 derives the speed of sound of theultrasonic wave that propagates along the bone front surface 10 a basedon the received wave signal of the leaky surface wave or the bonefront-surface refracted wave of the arrayed transducer 22 and the shapeof the bone front surface 10 a derived by the shape deriving module 82 dwhen the ultrasonic wave is transmitted from the transducer 21 dedicatedto wave transmission.

The bone strength index deriving module 84 derives an index related to astrength of the bone using the speed of sound in the two directions ofthe bone 10 derived by the speed-of-sound deriving module 83 and thethickness of the bone 10 derived by the shape deriving module 82 d.

The display module 9 is connected with the calculation module 8 todisplay the shapes of the bone front surface 10 a and the back surface10 b derived by the shape deriving module 82 d, and a diagnostic indexof the bone strength derived by the bone strength index deriving module84.

Next, an operation of the bone strength diagnostic device 1 is explainedparticularly focusing on an operation of the calculation module 8. FIGS.5 and 5B are a flowchart showing the operation of the bone strengthdiagnostic device 1.

As shown in FIGS. 5 and 5B, the arrayed transducer 22 performs wavetransmission and wave reception of ultrasonic waves (S1), and then, thetransducer 21 dedicated to wave transmission transmits an ultrasonicwave without moving the position of the ultrasonic transceiver 2 and theultrasonic wave is received by the arrayed transducer 22 (S2).

Shape Detection Step

The shape detecting module 82 derives a shape of the bone front surface10 a using the received wave signals of the arrayed transducer 22 whenthe ultrasonic wave is transmitted from the arrayed transducer 22.First, the incoming direction detecting module 82 a detects respectiveincoming directions of the front-surface reflected waves for the eleventransducer groups 22A-22K (S11).

Two incoming directions of the front-surface reflected waves for twoadjacent transducers constituting each transducer group (for example,the transducers 22 a and 22 b) are close to each other. Therefore, theincoming direction detecting module 82 a detects one incoming angle perone transducer group considering that the two incoming directions arethe same. Hereinafter, a method of detecting the incoming angle withrespect to the transducer group 22A is explained in detail.

As shown in FIG. 6A, it is assumed that the incoming angle of thefront-surface reflected wave 42 that reaches the transducer group 22A isset to θa. In this case, as shown in FIG. 6B, because the incomingangles of the front-surface reflected waves that reaches the twotransducers 22 a and 22 b is θa, a wave face 42 a of the front-surfacereflected waves 42 is inclined at the angle θa with respect to thearranged direction of the arrayed transducer 22 (the x-axis direction inFIG. 6B). Therefore, one front-surface reflected wave 42 reaches thetransducer 22 b after another front-surface reflected wave 42 reachedthe transducer 22 a, which further travels by a distance D. That is, thetransducer 22 b receives the front-surface reflected wave 42 after thetransducer 22 a. Here, the time difference between the times at whichthe two transducers 22 a and 22 b receive the front-surface reflectedwave 42 is set to Δt.

The following method may be used for deriving Δt based on the receivedwave signals of the transducers 22 a and 22 b. For example, the timedifference between maximum peaks of the received wave signals of the twotransducers 22 a and 22 b may also be used. Alternatively, so called the“zero-crossing method” may be used in which the time difference betweenintersecting point of rising parts of the maximum peaks of the receivedwave signals of the two transducers 22 a and 22 b with the line of zeroamplitude may also be used. Alternatively, a correlation processing witha waveform stored in advance in the calculation module 8 may also beperformed to derive the time difference Δt. Alternatively, a phasedifference between the received wave signals of the two transducers 22 aand 22 b may also be obtained by the quadrature detection method or thelike to derive the time difference Δt with the obtained phase differenceand the frequency of the incident wave. Note that this method can beused only when the phase difference between the received wave signals ofthe two transducers 22 a and 22 b is 180 degrees or less.

If the speed of sound in the soft tissues 11 is assumed to be Vs, thedifference D of the propagation course can be calculated by D=Vs*Δt. Asshown in FIG. 6B, when an interval between the two transducers 22 a and22 b is assumed to be W, the difference D of the propagation course canbe expressed by D=W*sin θa. Therefore, the incoming angle θa can becalculated by θa=arcsin (Vs*Δt/W). Although the measured value may beused for the speed of sound Vs in the soft tissues 11, an assumed valuemay also be used.

As described above, although the method of detecting the incoming angleθa of the front-surface reflected wave 42 with respect to the transducergroup 22A is explained, the incoming angles θa for other ten transducergroups 22B-22K may also be detected with a similar procedure.

When detecting the incoming direction, the incoming angle may bedirectly detected from the phase difference between the received wavesignals of two transducers constituting a transducer group. The termused herein “using the time difference between times at which thewave-reception transducers receive a front-surface reflected wave,respectively” of the incoming direction detecting module of thisembodiment also includes using a phase difference.

Next, the propagation time detecting module 82 b detects propagationtimes Ta after the ultrasonic wave is transmitted by the arrayedtransducer 22 until the front-surface reflected waves reach thetransducer groups 22A-22K using the received wave signals of the twotransducers 22 a and 22 b (S12). Although an average value of timesafter the ultrasonic wave is transmitted by the arrayed transducer 22until the front-surface reflected waves 42 reach the transducers 22 aand 22 b may be used for the propagation times Ta, values other than theaverage value may also be used. When the average value is used, errorsin the detected shape of the bone front surface 10 a can be reduced.

Next, the front-surface reflection point detecting module 82 c detectsthe front-surface reflection points on the bone front surface 10 a usingthe incoming angles θa and the propagation times Ta of the front-surfacereflected waves which reach the transducer groups 22A-22K, respectively(S13). Hereinafter, the method of detecting the position offront-surface reflection points on the bone front surface 10 a isexplained using the incoming angles θa with respect to the transducergroup 22A.

As shown in FIG. 6A, when the incoming angle of the front-surfacereflected wave 42 with respect to the transducer group 22A is θa, thisfront-surface reflected wave 42 is a reflection of the incidence wave41, which is transmitted from a point Ea on the surface of thetransducers 22 a-22 l and travels in the y-axis direction in FIG. 6A, toa point (front-surface reflection point) Ra on the bone front surface 10a inclined at θa/2 from the x-axis direction.

Here, as shown in FIG. 6A, the distance from the transducer group 22A inthe x-axis direction to the surface reflection point Ra is set to X, andthe distance from the transducer group 22A in the y-axis direction tothe surface reflection point Ra is set to Y.

Because the propagating direction of the incident wave 41 is the y-axisdirection, the distance from the point Ea to the surface reflectionpoint Ra is Y. In addition, because the distance from the surfacereflection point Ra to the transducer group 22A can be expressed byY/cos θa, the propagation distance La after the incident wave 41 istransmitted from the point Ea until the front-surface reflected wave 42reaches the transducer group 22A can be expressed by La=Y+Y/cos θa. Inaddition, the propagation distance La can be calculated by La=Vs*Ta fromthe propagation time Ta and the speed of sound Vs in the soft tissues.Therefore, Y can be calculated by Y=Vs*Ta*cos θa/(1+cos θa), and X canbe calculated by X=Vs*Ta*sin θa/(1+cos θa). Thus, the position of thesurface reflection point Ra can be detected.

The propagating direction of the ultrasonic wave (plane wave)transmitted from the arrayed transducer 22 is known beforehand.Therefore, even if it is not determined from which transducer thefront-surface reflected wave 42 received in the transducer group 22A istransmitted, the position of the surface reflection point Ra can bedetected by using the incoming angle θa and the propagation time Tawhich are detected.

As described above, the method of detecting the position of onefront-surface reflection point Ra is explained using the incoming angleθa and the propagation time Ta of the front-surface reflected wave thatreaches the transducer group 22A. However, the positions of the surfacereflection points Ra can be detected with a similar procedure for otherten transducer groups 22B-22K.

In the method described above, the average value of the propagationtimes of the front-surface reflected waves received by the twotransducers constituting a transducer group is set to be the propagationtime Ta. However, the propagation time of the front-surface reflectedwave received by one of the two transducers may be set to thepropagation time Ta as it is. In this case, it may be desirable to usetransducers of each transducer group that receive wave signals of thefront-surface reflected waves in the same spatial relationship. Forexample, when using the received wave signal of the transducer 22 b inthe transducer group 22A, the received wave signal of the transducer 22c is used in the transducer group 22B (in this case, the righttransducer of each group is used).

Further, two reflection points may be detected for one transducer groupusing propagation times and the incoming angle θa of the front-surfacereflected waves received by two transducers constituting the transducergroup. The term used herein “the propagation time of the front-surfacereflected wave that reaches each transducer group” of the propagationtime detecting module includes a case where the propagation times of thefront-surface reflected waves received by the two transducers are usedas “the propagation time of the front-surface reflected wave thatreaches each transducer group” as they are.

The shape deriving module 82 d derives a bone front surface line Ia inthe x-y plane as shown in FIG. 7 connecting the eleven surfacereflection points Ra detected by the front-surface reflection pointdetecting module 82 c with a straight line or a curve (S14). The bonefront surface line Ia is displayed on the display module 9 together witha bone back surface line Ib derived later. A size (outer diameter) ofthe bone 10 can be estimated by using the bone front surface line Ia.Note that the term used herein “deriving the shape of the bone frontsurface using a plurality of reflection points” by the shape derivingmodule is not limited to connecting a plurality of reflection points toderive the front surface line, but may include simply acquiring thespatial relationship of the plurality of reflection points.

Next, the shape of the bone back surface 10 b is derived. First, theincoming direction detecting module 82 a and the propagation timedetecting module 82 b detect an incoming direction θb and a propagationtime Tb0 of a back-surface reflected wave, respectively, that reacheseach of the transducer groups 22A-22K by a similar method as the case ofthe front-surface reflected wave 42 (S15, S16). Note that, because thereis a time difference as shown in FIG. 3 between the received wave signalof the front-surface reflected wave and the received wave signal of theback-surface reflected wave for each transducer, they are easilydistinguishable.

Next, the back-surface reflection point detecting module 82 e detectsthe position of the back-surface reflection point on the bone backsurface 10 b using the incoming direction θb and the propagation timeTb0 of the back-surface reflected wave that reaches each of thetransducer groups 22A-22K and the bone front surface line Ia derived bythe shape deriving module 82 d (S17). Hereinafter, the case whereback-surface reflection points on the bone back surface 10 b is detectedfor the transducer group 22A using the incoming angle θb and thepropagation time Tb0 is explained.

As shown in FIG. 7, an angle of refraction α1 in the bone front surface10 a of the back-surface reflected wave 54 is calculated from theincoming angle θb of the back-surface reflected wave 54 that reaches thetransducer group 22A and the bone front surface line Ia.

If the assumed value of the speed of sound in the bone 10 is Vb′, andthe angle of incidence of the back-surface reflected wave 54 to the softtissues 11 is α2, the relation of sin α1/sin α2=Vs/Vb′ can be satisfiedby Snell's law. From this equation, the angle of incidence α2 iscalculated, and the propagating direction (z-axis in FIG. 7) in the bone10 of the back-surface reflected wave 54 is derived.

Further, the angle of incidence β1 of the incident wave 51 to the bonefront surface 10 a is calculated from the propagating direction (y-axisdirection) of the incident wave 51 transmitted from the point Eb1 on thesurface of the transducers 22 a-221 to the bone front surface 10 a, andthe bone front surface line Ia.

If an angle of refraction of the incident wave 51 in the bone frontsurface 10 a is set to β2, a relation of sin β1/sin β2=Vs/Vb′ can besatisfied by Snell's law. From this equation, the angle of refraction β2is calculated, and as shown in FIG. 7, the propagating direction of theincident wave 51 in the bone 10 is derived. An intersecting point of thepropagating direction of the incident wave 51 in the bone 10 and thepropagating direction (z-axis) of the back-surface reflected wave 54 inthe bone 10 is set to K1.

Assuming that the intersecting point K1 is a reflection point on thebone back surface 10 b (back-surface reflection point), the incidentwave 51 transmitted from the point Eb1 would have reflected on the pointK1 in the bone back surface 10 b, and will have reached the transducergroup 22A. In this assumed propagation route, a predicted value of thepropagation time from wave transmission to wave reception is set to Tb1.Tb1 can be calculated from the propagation route of the ultrasonic wavefrom the point Eb1 to the transducer group 22A, using the speed of soundVs in the soft tissues 11 and the assumed value Vb′ of the speed ofsound in the bone 10.

In addition, for the incident waves 52 and 53 transmitted from thepoints Eb2 and Eb3 on the surface of the transducers 22 a-221, theintersecting points K2 and K3 of the propagating direction in the bone10 and the z-axis are also detected, respectively, similar to theincident wave 51. Further, the predicted values Tb2 and Tb3 of thepropagation time from the wave transmission to the wave reception arecalculated when the intersecting points K2 and K3 are set to theback-surface reflection point, respectively.

FIG. 8 shows a graph showing a relation between a position of theback-surface reflection points on the z-axis and the propagation time Tbfrom wave transmission of the incident wave until the back-surfacereflected wave reaches the transducer group 22A. A curve in FIG. 8connects three points acquired from the predicted values Tb1, Tb2, andTb3 of the propagation time when assuming the intersecting point K1, K2,and K3 to be the back-surface reflection points. A position of theback-surface reflection points Rb can be detected from an intersectingpoint of the curve and a line of Tb=Tb0 (actual measurement of thepropagation time).

When any of the predicted values Tb1, Tb2, and Tb3 of the calculatedpropagation time is almost equal to the actual measurement Tb0 of thepropagation time, the back-surface reflection points Rb can be detectedwithout using the graph as shown in FIG. 8.

As described above, only the method of detecting one back-surfacereflection point Rb using the incoming angle θb and the propagation timeTb0 of the back-surface reflected wave that reaches the transducer group22A is explained. However, a similar procedure can be applied to thedetection at a position of the back-surface reflection points Rb foreach of the remaining ten transducer groups 22B-22K.

The shape deriving module 82 d derives a bone back surface line Ib inthe x-y plane connecting the detected eleven back-surface reflectionpoints Rb with a straight line or a curve, as shown in FIG. 7 with adashed line (S18).

The derived bone back surface line Ib is displayed on the display module9 together with the bone front surface line Ia. Thus, an image of thebone can be obtained. Further, the shape deriving module 82 d derivesthe thickness of the bone 10 using the bone front surface line Ia andthe bone back surface line Ib (S19).

As explained above, the bone strength diagnostic device 1 of thisembodiment simultaneously transmits the ultrasonic waves of the samephase from the plurality of transducers 22 a-22 l constituting thearrayed transducer 22, and then derives the shape of the bone frontsurface 10 a and the back surface 10 b using the reflected waves.Typically, when ultrasonic waves are transmitted from the plurality oftransducers at shifted timing or phase from each other (i.e., whensending electric signals to the plurality of transducers at a shiftedtiming or phase), it may be necessary to have a plurality oftransmission circuits or change-over circuits. However, in thisembodiment, because ultrasonic waves of the same phase are simplytransmitted simultaneously from the plurality of transducers 22 a-22 l,it can achieve a configuration in which one transmission circuit 5 isconnected to the plurality of transducers 22 a-22 l. Therefore, thecircuit configuration of the transmission end will be comparativelysimple, and, as a result, its cost can be reduced.

In addition, because the ultrasonic waves are simultaneously transmittedfrom the plurality of transducers 22 a-22 l to detect the bone shape,the time required for the shape detection can be shortened compared withthe case where the bone shape is detected by transmitting the ultrasonicwaves from the plurality of transducers with the shifted wavetransmission timing. Therefore, shifting in the position of theultrasonic transceiver 2 can be reduced during the transceiving of theultrasonic waves and, thereby the bone shape can be detected withsufficient accuracy.

In addition, because the plurality of transducers 22 a-22 l areconfigured so as to perform both transmission and reception of theultrasonic wave, the number of transducers used for the transmission andreception of the ultrasonic wave for detecting the shape of the bone 10can be reduced, and the cost can be reduced as well.

Speed of Sound Deriving Step

Next, the speed-of-sound deriving module 83 derives a speed of sound inthe bone 10 using the received wave signals of the arrayed transducer 22when transmitting the ultrasonic wave from a transducer 21 dedicated towave transmission, and the shape of the bone front surface 10 a derivedby the shape deriving module 82 d. First, based on the shape of the bonefront surface 10 a, a transducer which receives a leaky surface wave isidentified from the plurality of transducers 22 a-22 l (S21).Hereinafter, it will be explained particularly.

As shown in FIG. 9, based on the spatial relationship of the transducer22 a, the transducer 21 dedicated to wave transmission, and the bonefront surface line Ia, a propagation course of the reflected wave fromthe bone front surface 10 a that reaches the transducer 22 a is detectedusing Feimat's principle. Fermat's principle states that an acousticwave which passes through two points propagates through the shortestcourse among the possible ones. According to Fermat's principle, thepropagation course of the reflected wave that reaches the transducer 22a will be the shortest course where a propagation distance from thetransducer 21 dedicated to wave transmission to the transducer 22 aamong the propagation courses of the reflected wave which can beestimated within a range of directivity of the transducer 21 dedicatedto wave transmission.

Next, the angle of incidence λ1 between the bone front surface 10 a andthe reflected wave that reaches the transducer 22 a is calculated. Then,from the assumed value Vb′ of the speed of sound in the bone 10 and thespeed of sound Vs in the soft tissues 11, an assumed value C of acritical angle is calculated so that this assumed value C of thecritical angle and the angle of incidence λ1 are compared. When theangle of incidence λ1 is smaller than the assumed value C of thecritical angle, a similar calculation is performed for each followingtransducers (the transducer 22 b and the transducers on the right of thetransducer 22 b), in the order of the closest to the farthest from thetransducer 21 dedicated to wave transmission, until the angle ofincidence is equal to (or greater than) the assumed value C of thecritical angle. Here, the angle of incidence λ3 in the propagationcourse of the reflected wave that reaches the transducer 22 c is assumedto be equal to the assumed value C of the critical angle. When the angleof incidence is equal to the critical angle, a surface wave occurs onthe bone front surface 10 a. Therefore, the transducer 22 d isidentified as the closest transducer to the transducer 21 dedicated towave transmission that receives a leaky surface wave. That is, thetransducer 22 d and the transducers on the right of the transducer 22 dare identified as the transducers which receive the leaky surface wave.

Note that, as described above, when the bone width (a diameter of thebone 10 in the horizontal direction of FIG. 1) is small, a transducer ata position apart from the transducer 21 dedicated to wave transmission(for example, the transducers 22 k and 22 l), may not be reached by theleaky surface wave. In this case, the closest transducer to thetransducer 21 dedicated to wave transmission that receives the leakysurface wave may be identified by the above-described method, and thelast transducer reached by the leaky surface wave may be identifiedusing the bone front surface line Ia (that is, a transducer capable ofreceiving the leaky surface waver, which is most distant from thetransducer 21 dedicated to wave transmission, may be identified).

Next, a waveform of the leaky surface wave (or the bone front-surfacerefracted wave) is detected from the received wave signals within apredetermined period of time from the wave transmission, measured bytransducers 22 d-22 l identified as the transducers which receive theleaky surface wave (S22). Hereinafter, this will be explained in detail.

Among the wave signals received by transducers 22 d-22 l, a waveform ofthe ultrasonic wave and a waveform of noise are distinguished to detecta waveform of the ultrasonic wave at the earliest wave-reception timing.Specifically, as shown in FIG. 10, a noise threshold N which is slightlygreater than a general noise level is set, and when amplitude exceedsthe threshold N consecutively at n points (for example, three points),it is determined to be a waveform of the ultrasonic wave, for example.

As described above, when both the leaky surface wave and the reflectedwave from the bone front surface 10 a reach one transducer, the leakysurface wave reaches before the reflected wave. Thus, by detecting thewaveform of the ultrasonic wave at the earliest wave-reception timing,the waveform of the leaky surface wave or the bone front-surfacerefracted wave can be detected. The propagation time of the leakysurface wave or the bone front-surface refracted wave which reached eachof the transducers 22 d-22 l can be derived from the waveform maximumpeak value, the zero-crossing value, etc. Note that, although the directwave may reach before the reflected wave and the leaky surface wave,because the direct wave is designed so that amplitude of which may bevery small compared with the reflected wave and the leaky surface waveas described above, the direct wave may be hardly detectable.

Next, the circumferential speed of sound of the bone front surface 10 ais calculated using the received wave signal of the ultrasonic wave atthe earliest wave-reception timing (the received wave signal of theleaky surface wave or the bone front-surface refracted wave) of thetransducers 22 d-22 l which are identified as transducers which receivethe leaky surface wave, and the shape of the bone front surface 10 a(S23).

First, one transducer group is selected from the plurality oftransducers 22 d-22 l identified as transducers which receive the leakysurface wave. Hereinafter, as shown in FIG. 11, a case where thetransducer group 22D having the transducers 22 d and 22 e is selectedwill be explained as an example.

First, the waveform of the ultrasonic wave at the earliestwave-reception timing detected from the received wave signals of thetransducers 22 d and 22 e (a waveform of the leaky surface wave or thebone front-surface refracted wave) is assumed to be the waveform of theleaky surface wave. The angle of refraction of the bone surfacerefracted wave from the bone front surface 10 a is very close to theangle of refraction of the leaky surface wave from the bone frontsurface 10 a (the same angle as the critical angle). Therefore, even ifthe waveform of the ultrasonic wave at the earliest wave-receptiontiming is a waveform of the bone front-surface refracted wave, the speedof sound can be derived with sufficient accuracy.

It is assumed that the incoming directions of the leaky surface wavesthat reach the two transducers 22 d and 22 e approximate with eachother, and an incoming angle θc1 of the leaky surface wave 35 withrespect to the transducer group 22D is detected from the time differencebetween the received wave signals of the leaky surface waves of the twotransducers 22 d and 22 e. As a particular method of detecting theincoming angle θc1, a similar method to the method of detecting theincoming angles θa and θb by the incoming angle detecting module may beused (refer to FIG. 6B).

An originating point P1 of the leaky surface wave 35 on the bone frontsurface 10 a is detected from the incoming angle θc1 and the bone frontsurface line Ia. An outgoing angle γ1 of the leaky surface wave 35 fromthe bone front surface 10 a is calculated from the normal direction atthe point P1 on the bone front surface line Ia and the incoming angleθc1. If a speed of sound in the bone 10 is set to Vb, a relation ofVb=Vs/sin γ1 can be satisfied by the Snell's law. From this equation,the speed of sound Vb of the ultrasonic wave (particularly, the surfacewave) that propagates along the bone front surface 10 a in thecircumferential direction can be calculated.

For all or some selected transducer groups among the plurality of thetransducer groups 22E-22K, the speed of sounds Vb in the bone 10 arecalculated similarly, and an average value of the plurality of speed ofsounds Vb is then calculated. Thus, the speed of sound in the bone 10can be derived with sufficient accuracy. The speed of sounds Vb derivedfor the transducer groups 22E-22K can also be mapped on the bone frontsurface line Ia.

As described above, the speed of sound in the bone 10 is calculatedusing the information on the shape of the bone front surface 10 a.Therefore, even if the shape of the bone front surface 10 a is curved,or even if the bone shape inclines to the contacting face 2 a, the speedof sound in the bone 10 can be derived with sufficient accuracy. As aresult, a diagnostic accuracy of bone strength can be improved.

As described above, although the circumferential speed of sound isderived, alternatively, the ultrasonic transceiver 2 may be installed sothat the arrayed direction of the arrayed transducer 22 is substantiallyin agreement with the longitudinal direction of the bone 10 to derivethe longitudinal speed of sound. Note that, because the same bonethickness derived when the cross-sectional shape perpendicular to thelongitudinal direction of the bone 10 is derived is used for thethickness of the bone 10, the shape of the bone back surface 10 b doesnot need to be additionally derived in this case.

Finally, after the speeds of sounds in the both directions are detected(S23B), the bone strength index deriving module 84 derives an indexrelated to the bone strength using the circumferential speed of soundand the longitudinal speed of sound which are derived by thespeed-of-sound deriving module 83, and the shapes of the bone frontsurface 10 a and the bone back surface 10 b detected by the shapedetecting module 82 (the shape deriving module 82 d) (S24). The derivedindex is displayed on the display module 9.

As described above, the bone strength diagnostic device 1 can obtain thethickness of the bone 10, the image of the bone 10, the circumferentialspeed of sound, and the longitudinal speed of sound, as the indexes ofbone strength or elements for deriving the indexes of bone strength.

Bone has an anisotropy structure in which it is stronger in thedirection of loads. In a macroscale, the bone has a long tubular-shapedfemur, tibia, or radius, and it has a structure strong against the loaddirection. In a microscale, bone has pores of substantially a circularcylinder shape of tens to hundreds of microns. The pores extendsubstantially in the load direction and, thus, the bone has a structurestrong against the load direction. In a nanoscale, bone has a structurein which biological apatite crystals surround collagen fibers. Thec-axis of collagen fibers or biological apatite crystals is oftenoriented in the load direction. Thus, it is important to examine thebone anisotropy structure when diagnosing bone strength.

Recently, it has been said that the bone strength can be expressed withtwo factors, the bone mass and the bone quality. In addition to the bonesize (outer diameter) and the bone thickness which represent the bonemass, examining the anisotropy structure leads to diagnosis of the bonequality.

First, for the bone strength, the bone size (outer diameter) and thecortical bone thickness that constitute the macro structure of acortical bone are important factors. As described above, the shapederiving module 82 d derives the thickness of the cortical bone 10 basedon the detected shapes of the bone front surface 10 a and the bone backsurface 10 b, and estimates the size (outer diameter) of the bone 10.Therefore, the index related to the bone mass can be derived by usingthe thickness of the cortical bone 10 and the size of the bone 10.

The speed of sound of the ultrasonic wave that propagates along the bonesurface in the circumferential direction is greatly affected by apercentage of pores, a pore size, and a pore connectivity thatconstitute the micro structure of cortical bone. These are factorsrelated to the bone density of the cortical bone. Therefore, the indexrelated to the bone density can be derived by using the circumferentialspeed of sound.

On the other hand, the speed of sound of the ultrasonic wave thatpropagates along the bone surface in the longitudinal direction isinfluenced by both the orientation of the biological apatite crystalsthat constitute the nanostructure of cortical bone, and the bone densityor pores that constitute the bone micro structure. Therefore, the boneanisotropy structure cannot be estimated only with the longitudinalspeed of sound, and the latter is insufficient for the diagnostic indexof bone strength. The index related to the bone orientation can bederived by using both the longitudinal speed of sound and thecircumferential speed of sound.

The speed of sound V of the ultrasonic wave which passes through insideof an object can be expressed by the following Equation (1), indicatingan elastic characteristic of the bone.

V=c√{square root over (c/ρ)}  (1)

Here, c is elastic stiffness and ρ is density.

Therefore, the circumferential speed of sound and the longitudinal speedof sound may also be used as the indexes of the bone strength as theyare. Because the speed of sound V represents an average elasticcharacteristic at both of the micro- and the nano-structure, it ischaracterized in that it can directly show the index of the bone qualityrelated to the bone strength, unlike with X-rays.

As described above, because the bone strength diagnostic device 1 canderive the plurality of indexes related to the bone strength, it ispossible to diagnose bone strength in more detail by using theseindexes. Note that only one or some of the indexes may be used in thisembodiment without using all of the indexes as the index of bonestrength.

Modified Embodiments

Next, modified embodiments to which various changes is made to theprevious embodiment will be explained. However, components having asimilar configuration to those of the previous embodiment are given withthe same reference numerals, and their explanation will be suitablyomitted.

Modified Embodiment 1

In the previous embodiment, both the circumferential speed of sound andthe longitudinal speed of sound are derived. However, the bone strengthmay be diagnosed by deriving only the circumferential speed of sound(the thickness of the cortical bone 10).

Modified Embodiment 2

The calculation module 8 may include a damping coefficient detectingmodule that detects a damping coefficient of the ultrasonic wavereceived by each transducer based on the transmitted wave signal of thetransducer 21 dedicated to wave transmission and the received wavesignal of each of the transducers 22 a-22 l. A particular operation inthis modified embodiment is explained below.

First, the damping characteristic detecting module calculates a spectrumof the leaky surface wave (or the bone front-surface refracted wave)received by each of the transducers 22 a-22 l and a spectrum of theultrasonic wave transmitted from the transducer 21 dedicated to wavetransmission with the Fourier transform to detect a spectrum ratio ofthe received wave signal of each of the transducers 22 a-22 l withrespect to the transmitted wave signal.

Generally, because the attenuation rate of the ultrasonic wave thatpropagates inside of a living body is greater in high-frequencycomponents of the ultrasonic wave than low-frequency components, thedetected spectrum ratio has a certain inclination. By calculating thisinclination, a damping coefficient (BUA: Broadband UltrasonicAttenuation [dB/MHz]) can be detected.

The detected damping coefficients (BUA) of the plurality of transducers22 a-22 l are displayed on the display module 9. By using the dampingcoefficients (BUA) of the plurality of transducers 22 a-22 l, the bonestrength can be diagnosed in more detail.

Modified Embodiment 3

The maximum amplitudes of the leaky surface waves (or the bonefront-surface refracted waves) received by the transducers 22 a-22 l maybe displayed on the display module 9, for example, and the bone strengthmay be diagnosed using these amplitudes.

Modified Embodiment 4

As the method of deriving the speed of sound in the bone 10, thefollowing method may also be used. First, two transducer groups (i.e.,two groups of transducers, each including a pair of transducers) areselected from the plurality of transducers identified as transducersthat receive the leaky surface wave. Preferably, the transducers to beselected do not overlap within the same transducer group or over thetransducer groups. Hereinafter, as shown in FIG. 12, a case where thetransducer group 22D having the transducers 22 d and 22 e, and thetransducer group 22H having the transducers 22 h and 22 i are selectedwill be explained as an example.

Similar to the previous embodiments, assuming that the waveform of theleaky surface wave or the bone front-surface refracted wave detectedfrom the received wave signals of the transducers 22 d, 22 e, 22 h, and22 i is the waveform of the leaky surface wave, The incoming angles θc2and θc3 of the leaky surface waves 36 and 37 to the two transducergroups 22D and 22H are detected, respectively.

The originating points P2 and P3 of the leaky surface waves 36 and 37 inthe bone front surface 10 a are detected from the incoming angles θc2and θc3, and the bone front surface line Ia, respectively. Then, adistance d1 from the transducer group 22D to the point P1, a distance d2from the transducer group 22H to the point P2, and a distance d3 betweenthe points P1 and P2 are calculated.

When the time difference between the times at which the two transducergroups 22D and 22H received the leaky surface waves 36 and 37 is set toΔTc, the time difference ΔTc can be expressed byΔTc=(d3/Vb)−{(d1−d2)/Vs} from the difference in the propagation routesof the ultrasonic wave that reaches the two transducer groups 22D and22H. The ΔTc can be calculated using the wave-reception timings of theleaky surface wave of the four transducers 22 d, 22 e, 22 h, and 22 i.Therefore, the speed of sound Vb in the bone 10 can be calculated fromthe equation of Vb=d3/{ΔTc+(d1−d2)/Vs}.

Modified Embodiment 5

As the method of deriving the speed of sound in the bone 10, thefollowing methods may also be used. First, one transducer group isselected from the plurality of transducers identified as transducersthat receive the leaky surface wave. Hereinafter, as shown in FIG. 13, acase where the transducer group 22D having the transducers 22 d and 22 eis selected is explained as an example.

Assuming that the waveform of the leaky surface wave or the bonefront-surface refracted wave detected based on the received wave signalsof the transducers 22 d and 22 e is the waveform of the bonefront-surface refracted wave, an incoming angle θc4 of the bonefront-surface refracted wave 38 with respect to the transducer group 22Dis calculated. Then, from the incoming angle θc4 and the bone frontsurface line Ia, an outgoing point (refracted point) P4 of the bonefront-surface refracted wave 38 in the bone front surface 10 a isdetected. Then, an outgoing angle (angle of refraction) γ4, between thebone front-surface refracted wave 38 and the normal direction at thepoint P4 on the bone front surface line Ia, is calculated from theincoming angle θc4 and the angle of the surface line Ia with thehorizontal axis.

The bone front-surface refracted wave 38 that propagates inside of thebone is generated by an ultrasonic wave 39 refracted on the bone frontsurface 10 a. When an angle of incidence of the ultrasonic wave 39 tothe bone front surface 10 a is φ, the speed of sound Vb in the bone 10(i.e., the speed of sound of the ultrasonic wave 39) can be expressed byVb=Vs−sin φ/sin γ4 by the Snell's law.

Next, based on the angle range of the ultrasonic wave transmitted fromthe transducer 21 dedicated to wave transmission, a position P5 of theleft end part in FIG. 13 is detected within the incident range of theultrasonic wave on the bone front surface 10 a. An angle of incidenceφmin is calculated assuming that the ultrasonic wave 39 propagates fromthe point P5 to the point P4. The point P5 can be at a position beyondthe range of the bone shape derived by the shape deriving module 82 d.In this case, the point P5 is detected using the bone shape predictedfrom the bone shape within the range derived by the shape derivingmodule 82 d.

The angle of incidence φ is an angle within a range from φmin to 90degrees. The speed of sound Vb is a speed ranging from Vmin (Vmin=Vs*sinφmin/sin γ4) to Vmax (Vmax=Vs/sin γ4). FIG. 14 is a graph showing arelation between the angle of incidence φ and a propagation time Tc fromwave transmission to wave reception. The curve in FIG. 14 shows thepropagation time Tc in the propagation course of each angle of incidenceφ when changing the angle of incidence φ from φmin to 90 degrees. Thepropagation time Tc at a certain angle of incidence φ is calculated fromthe propagation course length according to the angle of incidence φ, thespeed of sound Vb in the bone according to the angle of incidence φ, andthe speed of sound Vs in the soft tissues.

An actual measurement Tc0 of the propagation time is calculated from thereceived wave signals of the transducers 22 d and 22 e. An angle ofincidence φ0 is derived from an intersecting point of the curve of FIG.14 and the line of Tc=Tc0. The speed of sound Vb in the bone 10 iscalculated using the angle of incidence φ0. Thus, the speed of sound Vbof the ultrasonic wave that propagates inside of the bone 10 in thecircumferential direction (particularly, the ultrasonic wave thatpropagates in the vicinity of the bone front surface 10 a of the bone10) can be derived.

Modified Embodiment 6

In the previous embodiments, an ultrasonic wave is transmitted from thearrayed transducer 22, and after a predetermined period of time afterthat, another ultrasonic wave is transmitted from the transducer 21dedicated to wave transmission. However, the ultrasonic waves may besimultaneously transmitted from the arrayed transducer 22 and thetransducer 21 dedicated to wave transmission.

In this case, different transmission circuits may be connected to thearrayed transducer 22 and the transducer 21 dedicated to wavetransmission, so that ultrasonic waves of different frequencies may betransmitted from the arrayed transducer 22 and the transducer 21dedicated to wave transmission.

Modified Embodiment 7

Although the plurality of transducers that constitute the arrayedtransducer 22 perform both wave transmission and wave reception in theprevious embodiments, only some transducers among the twelve transducers22 a-22 l may be configured so as to perform the reception of theultrasonic wave. Particularly, for example, as shown in FIG. 15A, eighttransducers 22 a, 22 b, 22 d, 22 e, 22 g, 22 h, 22 j, and 22 k among thetwelve transducers 22 a-22 l may be connected with eight receptioncircuits to respectively perform the wave reception of the ultrasonicwaves (the number of transducers may depend on the configuration of thearrayed transducer). In this case, the incoming direction detectingmodule 82 a may determine four transducer groups 22L-22O where eachtransducer group is constituted with two adjacent transducers.

Modified Embodiment 8

Moreover, for example, as shown in FIG. 15B, alternately selected sixtransducers from the twelve transducers 22 a-22 l (for example, thetransducers 22 a, 22 c, 22 e, . . . , and 22 k) may only perform wavereception of the ultrasonic wave (the number of transducers may dependon the configuration of the arrayed transducer). In this case, theincoming direction detecting module 82 a may determine five sets oftransducers 22P-22T where alternately selected two transducersconstitute a transducer group.

According to the configurations of the Modified Embodiments 7 and 8, thenumber of reception circuits can be reduced comparing to the previousembodiments and, thus, the circuit configuration will be simplified andits cost can be reduced as well.

Modified Embodiment 9

A change-over circuit, such as an analog switch, may be provided betweenthe reception circuit and the arrayed transducer 22, and only sometransducers among the twelve transducers 22 a-22 l, which are connectedto the reception circuit through the change-over circuit may performwave reception (the number of transducers may depend on theconfiguration of the arrayed transducer). For example, as shown in FIG.15C, only one transducer among the twelve transducers 22 a-22 l may beconnected to the reception circuit 6 a through the change-over circuit106.

The change-over circuit 106 switches over sequentially from onetransducer to another, which is connected to the reception circuit, eachtime an ultrasonic wave is transmitted. By transmitting the ultrasonicwaves a total of twelve times, the received wave signals of the twelvetransducers 22 a-22 l can be acquired. Note that an illustration of acircuit configuration of the transmission end is omitted in FIG. 15C.According to this configuration, the number of reception circuits can bereduced compared to the previous embodiments and, thus, its cost can bereduced, while the received wave signals of the twelve transducers 22a-22 l can be acquired similar to the previous embodiments.

Modified Embodiment 10

In the previous embodiments, the plurality of transducers 22 a-22 lconstituting the arrayed transducer 22 perform both wave reception ofthe ultrasonic wave transmitted from the arrayed transducer 22 and wavereception of the ultrasonic wave transmitted from the transducer 21dedicated to wave transmission. However, without limiting to thisconfiguration, for example, four transducers 22 a-22 d on the side ofthe transducer 21 dedicated to wave transmission may perform only wavereception of the ultrasonic wave transmitted from the arrayed transducer22, and four transducers 22 j-22 l on the opposite side from thetransducer 21 dedicated to wave transmission may perform only wavereception of the ultrasonic wave transmitted from the transducer 21dedicated to wave transmission, and further, four transducers 22 e-22 hof the central part may perform wave reception in both cases of wavetransmission (the division in number of the transducers is not intendedto be limited and therefore any number can be selected to divide thetransducers in group).

In this case, eight reception circuits may be provided, and achange-over circuit may be provided between the eight reception circuitsand the arrayed transducer 22. In addition, the transducer that performswave reception may be switched according to the transducer thattransmits the ultrasonic wave (the transducer 21 dedicated to wavetransmission or the arrayed transducer 22). According to thisconfiguration, the number of reception circuits can be reduced comparedto the previous embodiments.

Modified Embodiment 11

Without providing the transducer 21 dedicated to wave transmission, anultrasonic wave may be transmitted obliquely to the contacting face 2 aby transmitting the ultrasonic wave whose phase may be controlled fromthe plurality of (for example, four) transducers at the end of thearrayed transducer 22.

According to this configuration, because the transducer 21 dedicated towave transmission is unnecessary, the configuration of the ultrasonictransceiver 2 includes only the arrayed transducer 22 and, thus it canbe simplified. Further, because the transducer 21 dedicated to wavetransmission is not provided, the number of transducers that constitutethe arrayed transducer 22 can be increased. Therefore, the range inwhich the bone shape can be detected will be wider. However, in thisconfiguration, a plurality of transmission circuits is needed and thecircuit configuration will be more complicated with an increased cost.Thus, the previous embodiments may be more preferred for this regards.

Modified Embodiment 12

In the ultrasonic transceiver 2 of the previous embodiments, althoughthe number of transducers 21 dedicated to wave transmission is one, thistransceiver 2 may be an ultrasonic transducer 202 including twotransducers 21 dedicated to wave transmission arranged in the samedirection as the arrayed direction of the arrayed transducer 22 as shownin FIG. 16A, for example. In this configuration, transducers thattransmit an ultrasonic wave are selected from the two transducers 21dedicated to wave transmission according to the thickness of the softtissues 11 and/or the size of the curvature of the bone front surface 10a. According to this configuration, the arrayed transducer 22 canreceive the leaky surface wave or the bone front-surface refracted wavemore reliably.

Modified Embodiment 13

Similarly, for example, as shown in FIG. 16B, the ultrasonic transceiver2 may be an ultrasonic transceiver 302 including two arrayed transducers22 arranged perpendicularly to each other, and two transducers 21dedicated to wave transmission arranged at the ends of the arrangeddirection of these two arrayed transducers 22. FIG. 16B is a plan viewlooking toward the contacting face 2 a.

According to this configuration, without changing the orientation of theultrasonic transceiver 302, a cross-sectional shape of the bone in thecircumferential direction and a cross-sectional shape in thelongitudinal direction can be detected, and the circumferential speed ofsound and the longitudinal speed of sound can be derived as well.Therefore, the measuring time can be shortened.

Modified Embodiment 14

For example, the ultrasonic transceiver 2 may be an ultrasonictransceiver 402 including an arrayed transducer 422 having a pluralityof transducers 422 a arranged in a 12×12 matrix as shown in FIG. 16C. Inthis figure, twelve transducers 421 a dedicated to wave transmission arearranged in the left-and-right direction in the upper part of thearrayed transducer 422 and twelve transducers 421 b dedicated to wavetransmission are arranged in the up-and-down direction on the left-handside of the arrayed transducer 422 Note that the number of transducersmay depend on the configuration of the ultrasonic transceiver 2.

According to this configuration, for example, from the right end of thematrix-arrayed transducer 422 in turn, using the twelve transducers 422a arranged in the up-and-down direction and the transducer 421 adedicated to wave transmission corresponding thereto, the bone shape isdetected similar to the previous embodiments to derive the speed ofsound in the bone using the detected bone shape. Accordingly, thethree-dimensional shape of the bone 10 can be derived. In addition, thespeed of sound of the ultrasonic wave that propagates in the up-and-downdirection at the twelve locations in the left-and-right direction can bederived (between 421 a and 422 a). Therefore, because the speed of soundin a certain direction can be measured at a plurality of locations, thespeed of sound of the ultrasonic wave in the bone can be derived withmore accuracy.

The speed of sound of the ultrasonic wave that propagates in theleft-and-right direction can be derived at twelve locations in theup-and-down direction by deriving sequentially from the upper end of thearrayed transducer 422, speeds of sound using the twelve transducers 422a arranged in the left-and-right direction and the transducer 421 bdedicated to wave transmission corresponding thereto arranged in theup-and-down direction.

Modified Embodiment 15

The shape detection module that detects the shape of the front surfaceof the bone 10 is not limited to the configurations of the previousembodiments. For example, it may be or may not be of a type using theultrasonic wave (for example, X-rays may be used instead). However, inthe case described above in which the shape detection module uses theultrasonic wave, a part of the configuration for deriving the speed ofsound (for example, the transmission circuit, the reception circuit,etc.) may be commonly formed with the shape detection module, andthereby its cost can be reduced.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims, including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has,”“having,” “includes,” “including,” “contains,” “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a,” “has . . . a,” “includes . . . a,” “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially,” “essentially,”“approximately,” “approximately” or any other version thereof, aredefined as being close to as understood by one of ordinary skill in theart, and in one non-limiting embodiment the term is defined to be within10%, in another embodiment within 5%, in another embodiment within 1%and in another embodiment within 0.5%. The term “coupled” as used hereinis defined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

1. A bone strength diagnostic device, comprising: a wave-transmissionmodule for deriving a speed of sound that transmits an ultrasonic wavefrom a wave-transmission transducer for deriving the speed of soundobliquely to a bone covered with soft tissues; a wave-reception modulefor deriving the speed of sound that receives the ultrasonic wave thatexits from the bone to the side of the soft tissues with a plurality ofwave-reception transducers for deriving the speed of sound, theultrasonic wave being received after it is transmitted from thewave-transmission module for deriving the speed of sound and propagatesalong a front surface of the bone; a shape detection module fordetecting a shape of the front surface of the bone; and a speed-of-soundderiving module for deriving the speed of sound of the ultrasonic wavethat propagates along the front surface of the bone based on thereceived wave signal by the wave-reception module for deriving the speedof sound, and the shape of the front surface of the bone detected by theshape detection module.
 2. The bone strength diagnostic device of claim1, wherein the wave-reception transducer for deriving the speed of soundincludes a plurality of wave-reception transducers for deriving thespeed of sound; and wherein a sound insulating material is arrangedbetween the wave-transmission module for deriving the speed of sound andthe plurality of wave-reception transducers for deriving the speed ofsound.
 3. The bone strength diagnostic device of claim 1 or 2, whereinthe shape detection module includes: a wave-transmission module forshape detection that transmits the ultrasonic wave to the bone; awave-reception module for shape detection that receives a front-surfacereflected wave of the ultrasonic wave from the front surface of thebone, the ultrasonic wave being transmitted from the wave-transmissionmodule for shape detection; and a front surface shape detecting modulefor detecting the shape of the front surface of the bone using the wavesignal received by the wave-reception module for shape detection.
 4. Thebone strength diagnostic device of claim 3, wherein thewave-transmission module for shape detection includes a plurality ofwave-transmission transducers for shape detection that transmit theultrasonic waves simultaneously; and wherein the wave-reception modulefor shape detection includes a plurality of wave-reception transducersfor shape detection that receive the front-surface reflected wave; andwherein the front surface shape detecting module includes: an incomingdirection detecting module for detecting an incoming direction of thefront-surface reflected wave to each transducer group using a timedifference between times when two wave-reception transducers for shapedetection constituting each transducer group receive the front-surfacereflected wave, each transducer group including adjacent twowave-reception transducers for shape detection among the plurality ofwave-reception transducers for shape detection; a propagation timedetecting module for detecting a propagation time of the front-surfacereflected wave that reaches each transducer group using the receivedwave signal of the front-surface reflected wave of at least onewave-reception transducer for shape detection among the twowave-reception transducers for shape detection constituting eachtransducer group; a front-surface reflection point detecting module fordetecting a reflection point of the ultrasonic wave on the front surfaceof the bone based on the incoming direction and the propagation time ofthe front-surface reflected wave detected for each transducer group bythe incoming direction detecting module and the propagation timedetecting module, respectively; and a shape deriving module for derivingthe shape of the front surface of the bone using the plurality ofreflection points on the front surface of the bone, the reflectionpoints being detected for the plurality of transducer groups havingdifferent transducers by the front-surface reflection point detectingmodule.
 5. The bone strength diagnostic device of claim 4, wherein thewave-transmission transducer for shape detection functions as thewave-reception transducer for shape detection as well.
 6. The bonestrength diagnostic device of claim 4, wherein the wave-receptiontransducer for deriving the speed of sound functions as thewave-reception transducer for shape detection as well.
 7. The bonestrength diagnostic device of claim 1, wherein the shape detectionmodule performs detection of a shape of a back surface of the bone inaddition to the detection of the shape of the front surface of the bone.8. The bone strength diagnostic device of claim 4, wherein thewave-reception module for shape detection performs wave reception of theback-surface reflected wave, that is reflected from the back surface ofthe bone and reaches the plurality of wave-reception transducers forshape detection after the front-surface reflected wave, in addition toperforming the wave reception of the front-surface reflected wave;wherein the incoming direction detecting module performs detection of anincoming direction of the back-surface reflected wave to each transducergroup using a time difference between times when the two wave-receptiontransducers for shape detection constituting each transducer groupreceives the back-surface reflected wave in addition to performingdetection of the incoming direction of the front-surface reflected wave;wherein the propagation time detecting module performs detection of thepropagation time of the back-surface reflected wave that reaches eachtransducer group using the received wave signal of the back-surfacereflected wave of at least one wave-reception transducer for shapedetection among the two wave-reception transducers for shape detectionconstituting each transducer group in addition to performing thedetection of the propagation time of the front-surface reflected wavethat reaches each transducer group; wherein the shape detecting moduleincludes a back-surface reflection point detecting module for detectinga reflection point of the ultrasonic wave on the back surface of thebone based on the incoming direction and the propagation time of theback-surface reflected wave detected for each transducer group by theincoming direction detecting module and the propagation time detectingmodule, and the shape of the front surface of the bone derived by theshape deriving module; and wherein the shape deriving module derives theshape of the back surface of the bone with the back-surface reflectionpoint detecting module using the plurality of reflection points on theback surface of the bone that are detected for the plurality oftransducer groups having different transducers.
 9. The bone strengthdiagnostic device of claim 1, further comprising a damping coefficientdetecting module for detecting a damping coefficient of the ultrasonicwave received by the wave-reception module for deriving the speed ofsound based on the transmitted wave signal of the wave-transmissionmodule for deriving the speed of sound and the received wave signal ofthe wave-reception module for deriving the speed of sound.
 10. A methodof diagnosing bone strength, comprising: detecting a shape of a frontsurface of a bone covered with soft tissues; transmitting an ultrasonicwave obliquely to the bone; receiving the ultrasonic wave that exitsfrom the bone to the side of the soft tissues at a plurality oflocations after it is transmitted and propagates along the front surfaceof the bone; and deriving a speed of sound of the ultrasonic wave thatpropagates along the front surface of the bone based on the receivedwave signal and the detected shape of the front surface of the bone. 11.The bone strength diagnostic device of claim 5, wherein thewave-reception transducer for deriving the speed of sound functions asthe wave-reception transducer for shape detection as well.
 12. The bonestrength diagnostic device of claim 2, wherein the shape detectionmodule performs detection of a shape of a back surface of the bone inaddition to the detection of the shape of the front surface of the bone.13. The bone strength diagnostic device of claim 3, wherein the shapedetection module performs detection of a shape of a back surface of thebone in addition to the detection of the shape of the front surface ofthe bone.